1. Field of Invention
The present invention relates to an electrical junction box suitable to be connected for example to a wire harness in a vehicle such as an automobile and a method of assembling the junction box.
2. Description of Related Art
Recently, the increase of electrical and electronic component parts which are mounted in a vehicle has led to increase of circuits to be accommodated in electrical connection boxes and junction boxes in the vehicle. Thus, when forming branch circuits at a high density, it is necessary to mount a large number of component parts on a junction box or the like, which causes increase of manufacturing complexity.
In a junction box disclosed in Japanese Laid-Open Patent Publication No. 2000-92660 and shown in FIG. 12, bus bars 5A-5D are laminated one upon another between an upper case part 2 and a lower case part 3, with insulation plates 4A-4E interposed between the bus bars 5A-5D. The upper case part 2 has a connector receiving portion 2a, a relay receiving portion 2b, and a fuse receiving portion 2c, on which in use connectors 6, relays 7 and fuses 8 are mounted respectively. Terminals of the connectors 6, the relays 7 and the fuses 8 are connected to tabs 5a projecting from the bus bars directly or are connected to the bus bars through relaying terminals. The lower case part 3 has also a connector receiving portion 3a to connect connectors to tabs projecting from the bus bars.
In the junction box 1, with the increase of the number of circuits, the area and the number of layers of the bus bars increase and thus the size of the junction box becomes large. If the connector, relay and fuse receiving portions are arranged on both the upper and lower case parts to connect connectors, relays and fuses to internal circuits of the junction box, it is possible to make the area of the junction box smaller than in the case where the receiving portions are mounted on only the upper case part or the lower case part.
However, if the connector, relay and fuse receiving portions are mounted on both the upper and lower case parts such that they are opposed vertically, the bent tabs of bus bars must overlap each other and thus cannot be easily arranged. In this case, it is necessary to form tabs on bus bars of other layers, which causes an increase of number of layers of bus bars, and thus leads to the increase of the height of the junction box. That is, the junction box is necessarily large.
Further, the above-described junction box is so constructed that the bus bars are connected to the connectors, the fuses and the relays. Thus, when the specification of the connection between the internal circuit and the fuses and/or the relays is altered, it is necessary to alter the entire internal circuit. Consequently the above-described junction box is incapable of allowing a circuit alteration easily.
Some proposals have been made for replaceable modules in electrical circuits of automobiles.
U.S. Pat. No. 5,179,503 shows a modular automobile power distribution box having replaceable modules carrying relays or fuses. The relays or fuses in each module are directly connected to terminals of leads of wire harnesses. A pair of bus bars connect power terminals to the fuses of three maxi-fuse modules. There is no discussion of interconnection of the modules.
U.S. Pat. No. 5,581,130 discloses removable multi-function modules in individual casings which are mounted on a circuit board. Each module is electrically connected to the power supply distribution layer of the board by a pin. Alternatively, three modules are shown connected together by two electrical and mechanical coupling bars.
It is an object of the present invention to provide a junction box which can be made thin without increasing the number of layers of bus bars to be accommodated therein and which can cope with a circuit alteration easily.
According to the present invention, there is provided an electrical junction box that provides electrical connection to a plurality of electrical connectors, a plurality of fuses and a plurality of relays. The electrical junction box includes
(i) a casing,
(ii) a connector circuit in the casing having at least one connector circuit insulation substrate and plurality of first bus bars fixed on the insulation substrate, the first bus bars being arranged to provide electrical connection to electrical connectors in use,
(iii) a fuse circuit in the casing having at least one fuse circuit insulation substrate, which is discrete from the connector circuit, and a plurality of second bus bars fixed on the fuse circuit insulation substrate, the second bus bars being arranged to provide electrical connection to fuses in use, and
(iv) a relay circuit in the casing having at least one relay circuit insulation substrate which is discrete from the connector circuit, and a plurality of third bus bars fixed on the relay circuit insulation substrate, the third bus bars being arranged to provide electrical connection to relays in use.
The first bus bars have respective welding portions standing up from the connector circuit insulation substrate and arranged alongside one another. The bus bars of one of the fuse and relay circuits have respective welding portions standing up from the respective insulation substrate and arranged alongside one another opposed to the welding portions of said first bus bars. A plurality of welded connections are formed by welding together of the opposed welding portions.
At at least one adjacent pair of the welded connections, one of the respective circuits provides an insulating partitioning member which is interposed between said pair of welded connections so as to prevent contact between the pair of adjacent welded connections.
Preferably, the welded portions are formed by bending an end of each of the bus bars perpendicularly to a surface of the insulation plate, the portions being arranged in parallel or coplanar.
According to the invention, there is also provided a method of assembling the electrical junction box described above. The method includes the steps of:
(i) arranging a first welding portions respectively to opposite second welding portions in position to be welded thereto at a plurality of welding locations, with at least one insulating partitioning member provided by one of the respective circuits interposed between an adjacent pair of the welding locations so as to prevent contact during welding between the welding portions of a first one of the pair of welding locations with the welding portions of the other of the pair of welding locations, and
(ii) after step (i), welding together the first and second welding portions at the respective welding locations.
The partitioning plate is erected on the insulation plate of the connector module or the fuse module and/or the relay module in such a way that the partitioning plate is inserted into a gap between the aligned welding portions of the connector module or the fuse module and/or the relay module.
The electrical junction box of the present invention has a modular construction. As described above, in the junction box of the present invention, the fuse circuit substrate and the relay circuit substrate are separately provided from the connector circuit substrate and are then joined by welding of the bus bars. This is in contrast with the conventional method, in which electrically conductive sheets are punched to form unitarily the connector connection circuit, the fuse connection circuit, and the relay connection circuit and form tabs to be connected to connectors, tabs to be connected to fuses, and tabs to be connected to relays and stacked in a single stack, the circuits thus being handled and arranged in a complicated manner. Consequently, the area of the bus bars increases and a large number of bus bars are necessary.
On the other hand, in the present invention, because the circuits are separately provided and welded, it is possible to avoid the complication of tabs overlapping each other and avoid a large number of bus bars. Thus, it is possible to form a thin or compact junction box. Further, because the circuits of the bus bars can be handled and arranged easily, the area of each bus bar can be reduced. Consequently, even though the bus bars are separately provided for the connector connections on the one hand and the fuse connections and the relay connections on the other hand, it is possible to reduce the total area of the bus bars and avoid increase of the area of the junction box.
Preferably, the connector module having the connector circuit, the fuse module having the fuse circuit, and the relay module having the relay circuit are all separately provided i.e. the respective insulation substrates are discrete from each other. Thus, if any one of the specification of the connector circuit, the fuse circuit, and the relay circuit is altered, the design of only any one of the modules need be changed. That is, the construction can cope with the alteration of the specification easily.
The first bus bars are provided separately from the second or/and third bus bars but connected thereto by means of welding. Thus this construction does not reduce reliability of the electrical connections. The welding portions may be connected to each other by ultrasonic welding, resistance welding, laser welding or gas welding.
When welding the welding portions to each other, a positioning portion of the partitioning plate is inserted into a gap between the arranged welding portions of the connector module or the fuse module and/or the relay module. Therefore, the welding portions are not dislocated and can be aligned and welded to each other, with the welding portions reliably held at a confronting position. Further, the partitioning plate partitions the welding portions from adjacent welding portions after they are welded to each other. Thus, there is no possibility that flexure of the welding portions causes adjacent welding portions to contact each other.
Preferably, the partitioning plate has an engaging portion which is positioned behind a rear surface of the welding portion of the connector module or the fuse module and/or the relay module and is capable of engaging the rear surface of the welding portion. Thereby, when welding the mating welding portions to each other, the engaging operation of the engaging portion prevents the mating portions from moving apart from each other. Accordingly, it is possible to maintain the position of the welding portions both longitudinally and widthwise.
Preferably, a supporting strip is provided on the insulation plate of the connector module or the fuse module and/or the relay module in opposition to both peripheral edges of the rear surface of the connector module or the fuse module and/or the relay module and the engaging portion of the partitioning plate is capable of engaging the rear surface of the welding portion of the connector module or the fuse module and/or the relay module through the supporting strip. This allows the superimposing position of the welding portions to be highly accurate.
Although the fuse circuit and the relay circuit may be separately formed, it is possible to integrate them with each other to form a fuse/relay composite circuit which receives fuses and relays on the same substrate which has bus bars for fuses and relays on it. In this case, if it is necessary to connect the circuit of any of the bus bars for fuses to any of the bus bars for relays, the respective bus bars are welded to each other or the bus bars may be integrally formed.